sin vultures a sina why is it negative ah

sin is a positive number in the coordinates of the first two quadrants.

The third and fourth quadrants are negative.

If it is in the first two quadrants.

Then + is the third and fourth quadrant sin( + is negative, so add a negative sign.

If it is in the third and fourth quadrants.

Located in the first quadrant of the second quadrant sin( + is positive, so add a negative sign.

Assuming a is the first quadrant angle, then vulture+a is the third quadrant angle.

The sin value is positive in the first quadrant and negative in the third.

It can be understood this way.

Here's a good note:

sin(煀+a) = sin vulcosa + sinacos vultures.

Because sin=0, cos=-1

So sin(煀+a)=-sina

sinx=f(x) is an odd function, i.e., f(-x)=-f(x), and its period is 2, i.e., half a period, which is obtained by the property of the periodic function (f(x+t 2)=-f(x)).

Below proves f(x+t 2)=-f(x)), assuming f(x+t 2)=-f(x)), so that x=y+t 2, substituting f(y+t)=f(-(y+t 2))=f(y), again.

f(-(y+t 2))=-f(y+t 2), so -f(y+t 2)=f(y), i.e. f(x+t 2)=-f(x)), so just let f(x)=sinx, you can get sin(v+a)=-sina

sina is not equal to sin(90-a), and the formula for sin(90-a) can be obtained by the sum of two angles: cos(90-a)=cos90*cosa+sin90sina=sina.

There is a quick memorization method for this (Qi Qi, who was taught by the teacher back then, still remembers it to this day.) Odd and even unchanged, symbols look at the quadrant. Specifically, for example, cos(a+k 2*pi), when it is 90+a, it can be regarded as being in the second quadrant.

cos is negative, so it is equal to -sinaWhen it's 180, the third quadrant, it's negative. Wait for the sale of -cosa when it is 270 Fourth quadrant, positive, sina

It seems so. Remember oh dear.

sin(2 +a) is equal to slow sina because sin is a periodic function with period 2. sin is a periodic function with period 2, so sin(pure modulo2 + sinWith the sum angle formula:

sin（2π+αsin2πcosα+cos2πsinα=sinα。

Assuming that a is the first elephant blind pants limit angle grinding resistance, then the acres brigade + a is the third quadrant angle.

The sin value is positive in the first quadrant and negative in the third.

It can be understood this way.

sin( -a)=sin(-a)=-sina is wrong in sin( -a)=-sin(-a), because of the odd change, the odd number is added to change the envy of the number brother and cover the file!

Therefore, sin( -a)=-sin(-a)=-sina)=sina

It should be like this: because 2 v-a belongs to the angle of the fourth elephant of the Cartesian coordinate system, and the sine of the angle of the fourth quadrant is negative, and because 2 vul-a and a of the first quadrant are hypothetical in relation to the pat tomb. That's why there is sin(2-a)=-sina.

sin(α±sinα·cosβ±cosα·sinβ

sina is a cycle of 2, and the pure crack is to sleepy pants to check sin(a-3) wang eggplant = sin(a-) sina